The present invention relates to alloys which can be used for producing dental castings, to dental castings, and to methods for making dental castings.
It is known to use casting alloys of the CoCrMo type, as they are standardized internationally according to ISO 5832/IV and, for example, according to the ASTM-F-75 nationally in the U.S.A. for the production of surgical implants. Because of their compatibility with the body and their mechanical hardness as a material for endoprostheses, such as, for example, artificial hip and knee joints, alloys of this type have proven their value.
In general, however, special demands are placed on alloys which are utilized in the dental industry. For example, firing alloys for metal ceramics must be compatible with commercial dental ceramics with respect to thermal expansion and contraction. These alloys, moreover, must form an oxide layer of minimal thickness to ensure adhesion between metal and ceramic. Also, for aesthetic reasons, the oxide color must not show through the opaque ceramic. In the case of dental casting pieces that cannot be masked, for example, removable prostheses with clamps, a certain activation capability and elastic temper is demanded. Beyond this, in the dental industry it is especially important that processing of the alloys being used can be done with materials readily available in the dental laboratory, that is, one should be able to be cast them with the usual casting centrifuges. For this reason the alloys, those which heretofore have been used in the dental industry, and those used as model casting material, have a far higher C-content than is permitted by the standard mentioned earlier. Firing alloys used in the dental industry are based mainly on an NiCr basis when it is a question of alloys of a type extremely free of noble metals.
Also, there are already known firing alloys which are based on CoCr. Compare, for example, DE 34 36 118, DE 33 09 909 A1 and EP 0 041 938. These alloys, however do not satisfy the demands which, according to the standards mentioned above, are placed on materials for the production of surgical implants.
Thus, for example, the CoCrMo alloy according to EP 0 041 938 contains 0.1 to 0.25% C, 0.1 to 3% Si and 0.1 to 8.0% Mn, where the high Mn and Si content levels are supposed to improve flow behavior. These high content levels are, however, not desirable in materials used in the production of surgical implants, that is, materials with which the present invention concerns itself. The alloy according to EP 0 041 938 contains 25 to 35 (preferably 27 to 33) % Cr, 3 to 8 (preferably 4 to 7) % Mo, up to 1% Fe, up to 0.3 (preferably up to 0.2) % Ni, and the remainder Co.
DE 33 00 909 discloses an alloy containing 0 to 0.3% C, 1 to 2% Si, 0 to 1.5% Mn, 20 to 35% Cr, 2 to 8% Mo, 0.3 to 2% Fe, 0.3 to 1.5% of Cer and/or Yt, and balance Co.
DE 34 36 118 discloses an alloy containing up to 2% C, 60 to 70% Co, 25 to 30% Cr and 3 to 7% Mo.